Irrigation device cuts water runoff

When tree deaths began to exceed normal rates in Manatee County's Flatford Swamp in 1998, environmentalists and Florida water managers suspected water runoff from nearby farms.

The excess irrigation water, they said, kept the swamp from drying out as it normally does each winter. The problem was common enough around the state to prompt University of Florida researchers to develop a solution: A buried irrigation system that reduces runoff and could maintain the swamps' normal water levels.

The system carries the added benefit of cutting water use by up to a third — something appealing to farmers nationwide.

In addition, while the system isn't designed to control nutrient runoff — another common problem — it may also reduce the amount of nitrates and other nutrients in surface water by encouraging growers to use less fertilizer, said Craig Stanley, a researcher at UF's Gulf Coast Research and Education Center where the system was developed.

“Growers normally have a fear of losing fertilizer that is leached away following a heavy rainfall,” Stanley said. “This system can provide better control of the water table level, meaning farmers can get by applying less fertilizer to their fields.”

Pacific Tomato Growers has installed the system on 90 acres it owns in Myakka City that drains water into the Flatford Swamp. Gary Bethune, Pacific Tomato's engineering director, said the company plans to expand its use in Florida as well as in California, Georgia and Maryland.

“We have had just extraordinary success with it,” Bethune said.

Known as enclosed seepage or sub-surface drip irrigation, the system uses a series of tubes buried 16 inches underground that carry water into the fields, said Stanley, a professor at the Bradenton center, which is part of UF's Institute of Food and Agricultural Sciences.

“The water table is typically close to the surface in flatwoods soils used for vegetable production, so irrigation is controlled by managing the level of the water table,” Stanley said. “The water from these tubes goes directly into the water table, causing it to rise to a level where it can get to the plants.”

Stanley said farmers have been using micro-irrigation techniques to deliver water directly to plants for years. But he said the new system's use of buried micro-irrigation tubing to manage water table levels makes it more efficient than prior systems by eliminating surface runoff.

“The system still requires as much maintenance and cleaning as above ground micro-irrigation systems, but it's a lot more forgiving system if a problem develops,” Stanley said. “The water goes to the water table instead of directly to the plant like in micro-irrigation.

“So if you get a clog somewhere in the tubing it's not a major problem because water keeps coming out someplace else in the system,” he said.

The Southwest Florida Water Management District had a priority of working with area growers to restore the swamp's natural water cycles, said Steven Minnis, senior community affairs coordinator with the district.

“We did not want to dictate a method growers should use to reduce or eliminate excess water flowing into Flatford Swamp,” Minnis said. “So we decided to begin partnership programs with the agricultural community within that particular basin.”

Bethune said while the system is saving Pacific Tomato Growers money in fertilizer and other areas, the savings do not yet offset the costs of the system itself. He estimated the cost for a similar system could run around $1,100 an acre, but he said he expects the cost to come down.

“One of the important things is going to be that the system is a permanent system, unlike conventional drip where we replace the drip tape on an annual basis,” Bethune said. “We're hoping that in the long-term the system will prove cost-effective.”